The exhaust gases coming out of the internal combustion engines contain particulate matter. This particulate matter in the environment is a well recognized health hazard of serious proportion. The finer the size of the particulate matter, the greater the chance it will remain suspended in air and, therefore, the more harmful are its impacts on both health and environment. The fine particulate matter generated by combustion of fuel carries with it substances that are known allergens, carcinogens and mutagenic agents. This fine particulate matter, because of its small size, travels deep into the respiratory tree, very often reaching the alveolar level, where it begins to cause serious diseases. Bronchitis, asthma, lung abbess and cancer have all, in a major part, been attributed to high levels of inhalable particulate matter in the atmosphere.
The consequences of fine particulate matter becomes much more severe because of its nature of not settling down and remaining in circulation in the air; it is often carried to high altitudes by convection currents. At cloud formation heights, this fine particulate matter acts as nuclei for water vapor condensation, forming clouds. The clouds so formed are heavier than the naturally formed clouds and are not sufficiently carried by the prevailing winds. Such clouds result in skewed distribution of rainfall such that some areas are subjected to very heavy and damaging downpour whereas others suffer drought like conditions.
Various methods have been attempted in the past to overcome the problem of particulate matter prevalent in the flowing gases, i.e. either in the exhaust stream of internal combustion engines or in the effluent gases in various industrial processes or furnaces.
One of the methods employed in the past enables internal combustion engines to use an array of sensors along with a microprocessor to ensure that the correct air-fuel mixture is maintained at all times and through all load conditions so as to get better combustion and thus, produce less particulate matter. The pre-treatment of fuel through temperature and chemical additives is another method that has been employed to achieve efficient combustion and hence, reduced particulate matter production.
The abovementioned methods pertain to the pre-ignition stage in the internal combustion engine. Once ignition occurs, all the exhaust matter needs to be pushed out of the cylinder so that the cylinder is ready and empty to accept the next air-fuel charge. The exhaust material is expelled out of the cylinder with a lot of noise and to reduce the noise, sound reducers or mufflers are put in line of flow of exhaust matter.
The catalytic converter, which is intended to convert harmful gases to less harmful ones, is also placed in line of flow of the exhaust matter.
It is further studied that any attempt to place a filter in line with the flow of exhaust increases the resistance to the flow of exhaust or causes backpressure in the flow. This prevents the engine cylinder from fully voiding itself of the exhaust gases generated by the ignition of previous air-fuel charge and is unable to perform an efficient combustion by not being able to accept the next pocket of air-fuel charge. Also, the increased resistance to flow of exhaust gases results in the loading of the engine i.e., the engine has to do more work in order to vent the exhaust material and this has a negative impact on fuel consumption. Further, the in-line filters get clogged with the particulate matter which need to be unclogged using some regenerative technology. During the process of regeneration, the particulate matter is expelled out and this particulate matter, being very fine in nature, is much more harmful.
Settling and momentum separators are also being used for removal of particulate matter from flowing gases wherein particles are collected by gravity and by their inertia, due to a sudden change in the direction of exhaust gases. Momentum separators are not effective because of the low mass of the particles involved.
There is another method known in the art for removing particulate matter from the flowing gases; namely cyclone or vortex separators which operate by incorporating centrifugal, gravitational, and inertial forces to remove particles suspended in air or gas. These types of separators use cyclonic action to separate particulates from a gas stream.
The most common type of cyclone separator used in industry is reverse flow type, wherein the gas enters through a tangential inlet at the top of the cyclone body, shaped to create a confined vortex gas flow and the clean gas exits through a central pipe.
Some of the major disadvantages with cyclone separators are that they have low efficiencies (particularly for small particles) and are unable to process “sticky” materials.
Some of the other methods used in the past include “Electrostatic Separators” and “Wet Collectors or Scrubbers”.
In view of foregoing, it is quite evident that all the above mentioned methods presently employed for removing particulate matter from flowing stream of gas are unable to separate the particulate laden gases in an effective and desired manner. Thus, it is a subject of immediate requirement to efficiently remove the particulate matter from the stream of flowing gases, especially the ones accompanying the exhaust of internal combustion engines and thereby reduce the harmful effects of particulate matter emitted in the environment.